Mercer discloses in his U.S. Pat. No. 3,281,897 an extrusion apparatus for extruding plastics tubing having two concentric sets of contra-rotating passages through which a plastics material flows during extrusion of the tubing. Mercer, however, unlike the applicants is not concerned with extruding a viscous material containing reinforcing fibres. When such fibres are included it has been found to be desirable that they should be orientated lengthwise of the extrusion passages so that when material issuing from the passages is wound helically the fibres will lie on helices of the opposite hand, the angles of which helices are controlled to give optimum burst strength and resistance to axial deformation of the finished tube. However, in Mercer's apparatus as shown in his FIGS. 5 and 6, the die entries comprise sharp edges and produce a sudden contraction of the flow at the entries of extrusion passages. The edges will generate vortices and hence cause turbulence in the viscous material due to the flow path of the material through the dies. Further, the sharp contraction of the flow on entry to the passages will produce a Vena Contracta in the flow downstream of the die entries which results in deceleration of the flow beyond the Vena Contracta with the result that the flow becomes turbulent. Moreover when fibres are included in the viscous material, they tend to engage the sharp edges and may be rotated to bridge the entry to the dies or tumble as they flow through the passages. Therefore the method and apparatus disclosed by Mercer although suitable for extruding a plastics material is not suitable for extruding such material when containing reinforcing fibres to produce a tube in which the fibres are orientated on helices of opposite hands having critical angles to give optimum strength to the tube.